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Asked by: gvr
Created at: 2025-08-02 01:36:47
Final Answer:
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Let's solve the series step-by-step:
Given series:
\[
\sum_{n=0}^{\infty} \frac{(2x-3)^{2n+1}}{\left(\frac{3}{2}\right)^n}
\]
### **Step 1: Rewrite the General Term**
\[
a_n = \frac{(2x-3)^{2n+1}}{\left(\frac{3}{2}\right)^n}
= (2x-3)^{2n+1} \cdot \left(\frac{2}{3}\right)^n
= (2x-3) \cdot \left[(2x-3)^2 \cdot \frac{2}{3}\right]^n
\]
### **Step 2: Identify as a Power Series**
Let \( y = (2x-3)^2 \cdot \frac{2}{3} \), so the series is:
\[
\sum_{n=0}^{\infty} (2x-3) \cdot y^n
\]
But since the first power is odd, let's focus on the root or ratio test for the original form.
### **Step 3: Use the Ratio Test to Find Radius and Interval of Convergence**
Let’s use the root test (easier for powers):
\[
\lim_{n \to \infty} \sqrt[n]{|a_n|}
= \lim_{n \to \infty} \sqrt[n]{|(2x-3)^{2n+1}|} \cdot \sqrt[n]{\left(\frac{2}{3}\right)^n}
= |2x-3|^2 \cdot \frac{2}{3}
\]
For convergence, we need:
\[
|2x-3|^2 \cdot \frac{2}{3} < 1
\]
\[
|2x-3|^2 < \frac{3}{2}
\]
\[
|2x-3| < \sqrt{\frac{3}{2}}
\]
\[
-\sqrt{\frac{3}{2}} < 2x-3 < \sqrt{\frac{3}{2}}
\]
So:
\[
3 - \sqrt{\frac{3}{2}} < 2x < 3 + \sqrt{\frac{3}{2}}
\]
\[
\frac{3 - \sqrt{\frac{3}{2}}}{2} < x < \frac{3 + \sqrt{\frac{3}{2}}}{2}
\]
**Interval of convergence:**
\[
\left( \frac{3 - \sqrt{3/2}}{2}, \frac{3 + \sqrt{3/2}}{2} \right)
\]
**Radius of convergence:**
\[
R = \frac{\sqrt{3/2}}{2}
\]
---
### **Step 4: Absolute and Conditional Convergence**
The series converges absolutely **inside** the interval (excluding endpoints).
To check for **conditional** convergence, check the endpoints:
#### **Check \( x_1 = \frac{3 - \sqrt{3/2}}{2} \):**
At this point, \( |2x-3| = \sqrt{3/2} \), so the general term becomes:
\[
a_n = (\pm \sqrt{3/2})^{2n+1} \cdot \left(\frac{2}{3}\right)^n = (\pm 1)^{2n+1} \cdot (\sqrt{3/2}) \cdot 1^n
\]
But \( (\pm 1)^{2n+1} = \pm 1 \), so \( a_n \) does **not tend to zero**; it oscillates and doesn't diminish. **So it diverges at endpoints.**
#### **Check \( x_2 = \frac{3 + \sqrt{3/2}}{2} \):**
Similar reasoning as above, the term does not go to zero.
**So, the series does not converge conditionally at any point; it only converges absolutely inside the interval.**
---
## **Final Answers:**
### (a) The interval of convergence is:
\[
\left( \frac{3 - \sqrt{3/2}}{2}, \frac{3 + \sqrt{3/2}}{2} \right)
\]
The radius of convergence is:
\[
\frac{\sqrt{3/2}}{2}
\]
### (b) The series converges absolutely on:
\[
\left( \frac{3 - \sqrt{3/2}}{2}, \frac{3 + \sqrt{3/2}}{2} \right)
\]
### (c) For what values of \( x \) does the series converge conditionally?
\[
\boxed{\text{B. The series does not converge conditionally.}}
\]
---
**Boxed summary for direct input:**
- (a) Interval of convergence: \(\left(\frac{3-\sqrt{3/2}}{2}, \frac{3+\sqrt{3/2}}{2}\right)\)
- Radius of convergence: \(\frac{\sqrt{3/2}}{2}\)
- (b) Absolutely: \(\left(\frac{3-\sqrt{3/2}}{2}, \frac{3+\sqrt{3/2}}{2}\right)\)
- (c) **B. The series does not converge conditionally.**
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